Electron beam controlling apparatus



Feb. 14, 1961 B. R. CLAY ELECTRON BEAM CONTROLLING APPARATUS Filed Aug. 31. 1955 3 Sheets-Sheet 1 INVENTOR. 50070 R (2/2) ATTOR/Vf) Feb. 14, 1961 B. R. CLAY ELECTRON BEAM CONTROLLING APPARATUS 3 Sheets-Sheet 2 Filed Aug. 31. 1955 r. V MM H MJVIML'NT I N V EN TOR. 60070 R 62/ BY v fim '6.

Feb. 14, 1961 a. R. CLAY 2,972,073

ELECTRON BEAM CONTROLLING APPARATUS Filed Aug. 31. 1955 3 Sheets-Sheet 3 IN V EN TOR.

y fix m United States'Patent ELECTRON BEAM CONTROLLING APPARATUS Burton R. Clay, Woodbury, N.J., assignor to Radio Corporation of America, a corporation of Delaware Filed Aug. 31, 1955, Ser. No. 531,705

10 Claims. (Cl. 313-77) The present invention relates to new and improved apparatus for use in controlling electrons in cathode ray tubes of the type employed as color television image reproducing devices. Specifically, the invention relates to apparatus for use in conjunction with cathode ray tubes having a plane of deflection at which electrons are subjected to a scanning movement in their travel toward a screen unit of the type comprising a mosaic screen and one or more adjacent grills or masks through which electrons pass in different angular directions to preselected elemental areas of the mosaic.

While the present invention is described herein as applied to a cathode ray tube of the dot-screen variety disclosed in an article by H. B. Law A Three-Gun Shadow-Mask Color Kinescope (October, 1951, issue of Proceedings of the I.R.E.), its applicability is not so limited, since the invention may also be employed with other types of cathode ray tubes wherein the angle of approach of an electron beam toward a mosaic screen determines its point of contact with the screen.

As described in the cited Law article, the particular screen area which is illuminated at any given instant in a cathode ray tube of the type in question is a function of the precise angle at which the electron beam approaches the color screen. When such tubes are manufactured in accordance with present-day mass production methods, it is not always possible to maintain the necessary accuracy in the assembly of the grill or mask and the phosphor screen. By virtue of such difficulties, many cathode ray tubes which are otherwise satisfactory in structure must be rejected because of color dilution. One particular form of color dilution which is encountered in color kinescopes is that which results from misalignment of the shadow mask or grill about its longitudinal axis with respect to the phosphor screen, this form of color dilution being termed tangential or rotational color dilution. Another form of color dilution is that-which results from radial misalignment of shadow mask or grill and screen such that the electrons strike a pointon the screen radially displaced from their desired point of impingement and which may be termed radial color dilution. Still another source of difiiculty in the operation of color kinescopes of the type under consideration is that which is brought about by stray magnetic fields such, for example, as the earths magnetic field andwhich may be tangential and/or radial in nature. 1

It is, therefore, a primary object of the present invention to provide new and improved apparatus for preventing color dilution of the type stemming from rotation and/ or radial misalignment of the tube parts and/or from magnetic fields.

In view of the foregoing, there have been proposed arrangements involving a plurality of magnets located around the screen region of the kinescope, each magnet being adjustable in strength and direction of intensity. According to certain prior arrangements, permanent magnets have been disposed with their axes of rotation "ice oriented radially of the kinescope. In the case of such apparatus, tangential error resulting from ambient magnetic fields parallel to the longitudinal axis of the tube is corrected by bucking or cancelling the undesired field by an equal but opposite field fromthe corrective magnet. A problem presented by such prior arrangements, however, is that of manipulating the magnets about their radial axes for adjustment purposes, so that special receiver cabinets permitting access to the magnets have been required in certain instances.

In general, the present invention provides means for subjecting the electron beams, in the space between the tubes shadow mask and target screen to substantially constant direct current magnetic fields of such intensity, polarity and orientation as to direct said electrons to their normal or intended points of impact on the screen, regardless of the section of the. screen in which the beams may be operating. In accordance with a specific illustrative embodiment of the present invention, such direct current magnetic field producing means comprises a plurality of permanent magnets having north and south poles and disposed around the screen unit of the cathode ray tube. Each magnet is supported rotatably about an axis which is parallel to the longitudinal axis of the tube so that the direction of flux from the magnet may be adjusted. Means are additionally provided for efiectively controlling the intensity of the fields of the permanent magnets. As will be more fully appreciated, adjustment of the magnets as to strength and polarization may be simply accomplished from the front of the cabinet in which the kinescope is housed.

Additional objects and advantages of the present invention will become apparent to those skilled in the art from a study of the following detailed description of the accompanying three sheets of drawings in which:

Figure 1 is a side elevational view, partially in section, of a three-gun tri-color kinescope of conventional construction which is provided, in accordance with one form of the invention, with novel electron beam pathcontrolling apparatus;

Figure 2 is a diagrammatic illustration of a cathode ray tube oriented with respect to certain axes to be described;

Figure 3 is a fragmentary front view, greatly enlarged, of the'screen of the tube of Figure 1;

Figure 4 is an isometric view of one of the magnets of Figure 1;

Figures 5a and'5b are partly schematic front end and side elevational views, respectively, of the tube and magnet assembly of Fig. 1; the drawings being markedto illustrate the direction of beam movement when subject to a magnetic field of a certain orientation;

Figs. 6a and 6b are views similar to those of Figs. 5a and 5b, respectively, but with a magnetic field of another orientation;

Figure 7 is an' isometric view of a television receiver cabinet showing a manner in which access to the magnets of Figure 1 may be had;

Figure 8 is a sectional view taken along line 8-8 of Figure 7; and

Figure 9 is a section along line 9-9 of Figure 7;

7 Referring to Figure 1 of the drawing, the color kinescope 10 shown therein comprises an evacuated envelope having a cylindrical neck portion 12 of glass, for example, which terminates in a flared cone portion 14 whose larger end is closed by a' glass face plate 16 through which is visible the phosphor screen 18 of the target structure of the tube which further includes a shadow spots at the target screen.

the drawing, the phosphor screen is deposited directly upon the rear surface of the face plate 16 and the mask 20 is curved approximately like the curvature of the face plate. Specifically, the screen 18 is provided on its rear 'sur'fac'e with a multiplicity of groups of red R), blue (B) and green (G) phosphor dots, the dots of each group being arranged at the apices of an equilateral triangle. The mask element 20 of the screen unit comprises a thin metal plate containing a multiplicity of ap- "ertures arranged in the same triangular pattern 'as the trios of phosphor dots such that there is one mask aperture for each trio of phosphor dots. The aperture mask 20 is supported in spaced relationship with respect to 'the' screen 18 by suitable means (not shown). Such a tube is described in detail in an article entitled, Development of a 21-inch Metal Envelope Color Kinescope by Seelen et al. which appeared in the March, 1955, is sue of RCA Review.

The cylindrical neck portion 12 of the kinescope 1i h'ouse sthree electron guns 24,16 and 28, each of which produces an electron beam intended for bombardment of a particular screen color. The guns 24, 26 and 23 may be arranged at the apices of an equilateral triangle as shown in the Law article or in any other suitable manher such, for example, as an in-line arrangement. The electron beams produced by the guns are indicated diagrammatically by the dotted lines 30, 32 and 34 and are focused in a conventional manner by suitable means -md1cated as an electromagnetic focus coil 36 energized by currents from a source 38, whereby to provide fine The electron beams are subjected to the action of substantially perpendicular maginetic fields for the scanning, in horizontal and vertical directions, of a conventional rectangular raster at the screen unit. Such scanning fields are produced by means erence will be made to the'X, Y and Zaxes of the kinescope 10. In order to facilitate an understanding of jsuch designations, Figure 2 illustrates, in simplified form,

the kinescope oriented about its several axes X, Y and Z. -It willbe seen from Figure 2 that the Z-axis coincides with the longitudinal axis of the tube, while =the X and Y-axes are normal to each other and to the Z-axis. I 7 As has been stated generally supra, one object of the present invention is that of eliminating the so-called tangential color dilution which results from a situ- 1 ation tantamount to that which exists when the shadow mask of a screen unit is rotationally displaced with respect to the phosphor screen (about their common axis). Figure 3 illustrates a front view of such screen unit, showing a typical case of tangential dilution. It will be understood that the three beams 3t 32 and 34 are intended to converge at the shadow mask and diverge therefrom so that the red beam 36 strikes the red-designated phosphor R and the other beams 32 and 34 strike the green and blue-designated phosphorsfG and B, respectively, which phosphor'dots are arranged, as explained, at the apices of an equilateral triangle. Assummg that there is some rotational mislocation of the shadow mask 20 and screen 18 or that there exists amagnet- 1c. held in the path of the beams between the shadow mask and phosphor-screen unit such that components of the-magnetic field are parallel to the Z axis'of' the tube, color d1lut1on of the tangential type will result. Thus, referring to Figure 3 wherein it is assumed; for'purposes is on and thatonly the red screen dots R are intended ,4 to be struck by electrons, the tangential color dilution is manifest at peripheral regions of the screen such that the red beam spots are not centered exactly on the red phosphor dots. Rather, the red beam spots are tangent to or overlap and, hence, illuminate peripheral portions of the adjacent blue and green phosphor dots, thus diluting the red light and preventing it from appearing with its proper degree of saturation.

While not illustrated in the drawing, it will be understood that radial color dilution, such as may result from a radial misalignment between the shadow mask 20 and screen 18, would be manifested by the beam spots being shifted laterally (i.e., horizontally or vertically) from its desired point of impingement, and that the beam spot intended for illumination of a red phosphor dot might instead land on an adjacent blue or green dot.

The present invention eliminates or, at least, substantially minimizes both forms of color dilution through the agency of means for subjecting the several electron beams to the action of substantially constant (i.e., DC.) magnetic fields (axial or transverse, for tangential or radial errors, respectively) in their travel between the shadow mask 20 and the phosphor screen 18. The intensity and polarity of the field are chosen so as to divert the electrons from their predetermined angularly related paths to other angular directions as required to direct them tov their intended points of impact upon the phosphor screen 18.

Figure 1 illustrates means, in accordance with a Specitic form of the invention, for providing the requisite axial or transverse magnetic field, such means comprising a plurality of permanent magnets 50 disposed around the screen unit of the tube 10. The number of magnets thus employed may varyybut the illustrative embodiment shown herein includes six magnets which may be equi-spaced about the screen region of the tube, three on each side of its vertical centerline; The manner in which these magnets perform their functions of minimizing tan gential and radial color dilution will be explained later. At this point, one of the magnets will be described in detail in connection with Figure'4;

The permanent magnet 59 is illustrated in Figure 4 as a'bar magnet magnetized along its longitudinal axis and having north and south poles designated N and S. A threaded bolt is secured to the magnet 59 as by means of a rivet 72 (Figure 8) so that it is per pendic'ular to the magnet. vThebolt 70 is slidably re ceived by a bushing 74 which is securely held in shap er-ture located centrally of a cup 78. The'end of the bolt 70 remote from the magnet 50 is prpvidedwitha screwdriver slot 80. The bushing 74 is slotted throughout a portion of its periphery as 'at 86. A generally triangular friction spring 88 (Fig. 4') which surrounds the bushing communicates with the bolt 70 through the slot Y 36 and engages the bolt. Thus, as will be understood, the spring 88 is in engagement with the threads of the bolt 70, so that when the bolt is rotated, it will thread its way toward or away from the cup 73.. Alternatively,

of simplicity of description, that only the red beam 36 the threads.

the bolt may be" pulled or pushed through the bushing 74 along its axis, which movement is permitted -by the expansion of the spring-88 as it is carnmed-outwardly by The cup 78 is formed of iron or other magnetic inaterial and is of internal diameter sufiicientto receive the magnet 50, Of the assembly thus far described, all of the'members with the exception of the magnet and 'cup 78 may be of any suitable non-magnetic material. The cup 78 is supported, with respect to't'netube, in a manner to be described; sothatthe magnet 58 is rotatable about an axis parallel to the longitudinal axis ofthe tube and ismovable alongtheZaXisofthe bolt 70.

When the magnet is in its extreme; retracted position '5 Zero. 011 the other hand, when the magnet 50 is in its extended position (as in Figure 4), the strength of the field produced by the magnet is at its maximum value. For positions of the magnet intermediate the two described extreme positions, proportionately difi'erent field strengths may be obtained.

Figure 5a illustrates diagrammatically a front view of the kinescope showin' a plurality of magnets 50 disposed around the screen region of the tube. The magnets 50 may be located as shown in Fig. 5a or may be disposed three on each side of the vertical center line of the tube, for example. As shown in Fig. So, each of the magnets 50 is rotatable about the axis of its associated bolt 70, the bolts 79 being parallel to the longitudinal axis of the kinescope. The uppermost magnet 50 in Fig. 5a is disposed with its north and south poles oriented along a line which is parallel to the X-axis of the tube. That is to say, the magnet in question will be understood as being tangential to the tube. Several of the flux lines of the magnetic field produced by the magnet 50 are also shown in the drawing. The fiux lines 90 are generally parallel, in the region of the tube screen unit, to the X-axis of the tube, so that an electron beam within the field of the flux lines 99 will be caused to move along the radial line 92, since the electron beam sees a transverse field, as shown in Fig. 5b, wherein the electron beam is indicated diagrammatically in a defiected position by the line 94. The direction of radial movement of the beam may be reversed by rotating the magnet 50 180 about the axis of the bolt 70, thereby reversing the direction of the magnetic field.

The use of the magnet 50 as described in connection with Figs. 5a and 5b affords a corrective magnetic field insofar as radial color dilution is concerned, since the field is efiective to move the electron beams of the kinescope radially of the tube as explained. Such corrective action of the magnets, moreover, may be employed regardless of whether the radial color dilution error results from a magnetic field which is transverse of the tube or radial misalignment of the tube parts. it will further be recognized that the intensity of the corrective field produced by any one of the magnets maybe adjusted by moving the magnet axially toward and away from its associated magnetic cup 78 (not shown in Figs. 5a and 51;). Thus, if no corrective action is required in any given sector of the tube, the magnet associated with that sector may be moved axially to its retracted position within its cup 78 so that the field of that magnet is effectively short-circuited by the cup.

Figs. 6a and 6b are views corresponding, respectively, to those of Figs. 5a and 511 but illustrating the orientation of oneof the magnets 59 for the minimization or elimination of tangential error such as that which results, for example, from the presence of a magnetic field whose lines of flux are generally parallel to the Z-axis of the kinescope. In the interest of simplicity, only one magnet is shown in each of Figs. 6a and 6b, but it will be understood that additional magnets are present as shown in the preceding figures. the magnet 51 is illustrated as disposed with its north and south poles oriented along a line which is radial of the tube 10. Flux lines traveling from the north pole N of the magnet 50 are indicated by'the reference numeral 90. As is known, the flux lines branch out, as shown by the flux lines 90a and 90b around the magnet, in return- ,ing to the south pole thereof. The effective field component of the magnetic field produced by the magnet 54 -is represented by the dotted line 96. The effective field component will be understood, therefore,as being radial of the tube, so that an electron beam in the region of the field is moved tangentially, as represented by the line 98. The direction in which the beam is thus moved tangentially by the field of the magnet 59 maybecontrolled by rotating the magnet about the axis of its bolt 70 by 180 in order to reverse the direction.

in the front'view of Fig. 6a}

Since the flux lines of'the field produced by the magnet are present in three dimensions, Fig. 6b shows the lines of flux in a plane drawn through the Y- and Z-axes. In Fig. 6b, the flux at the north pole of the magnet 59 is again represented by the reference numeral 96, the branch flux being indicated by reference characters 90c and 90d. The elfective component of the magnetic field is shown in Fig. 6b by the dotted line 96, which component will be understood as being perpendicular to the Z-axis of the tube. Since, as stated, the orientation of the magnet 50 in Figs. 6a and 6b produces tangential movement of the electron beams in the tube for the purpose of correcting for tangential error, it should be recognized that the correcting field is one which is perpendicular to the offending field. That is to say, and as has been explained, tangential error in such a tube is produced by a magnetic field whose lines of force are parallel to the Z-axis of the tube. The tangential error results, specifically, from the fact that the beam, in its deflected position, sees the Z-axis field components as transverse and is, therefore, deflected in a direction tangential of the tube. It is important to note, in this connection, that the correction for tangential error as effected by the present invention does not involve the provision of a tangential field which is equal to and opposite from an offending Z-axis field. Rather,

the correcting field is in quadrature with the offending or error-producing field. This latter fact is illustrated in Fig. 6b wherein the error-producing field is repre sented by the arrow 100.

The use of a quadrature field for the correction of tangential error in accordance with the present invention affords the advantage that the control of the magnet (both directional and intensity-wise) may be had from in front of the cathode ray tube. This is to be contrasted with prior art arrangements in which tangential error is corrected through the use of a bucking tangential field and in which control of the correcting magnets is had through rotation of each magnet about a radius of the tube.

The important advantage of having the control of each magnet in the form of a shaft which extends parallel to the longitudinal axis of the tube is clearly illustrated in Fig. 7 which shows a typical color television receiver cabinet 1G2. I I

lnFig. 7, the decorative bezel 194 has been-removed from its usual position to reveal the slotted ends of the magnet shafts 70 which project forwardly outside of the safety glass plate 196. Rotational movement of each of the magnets located within the cabinet 102 may be effected as by means of a screw driver 108 which engages the slotted end of the magnet shaft. Axial movement of the magnets may be effected by pushing or pulling the shaft 70, as explained above. Once the adjustment of the magnets has been completed, the bezel 164 may be returned to its proper place by snapping the spring fingers 118 into slots 112 in the front wall of the cabinet 102. i

in the interests of completeness of description, Figs. 8 and 9 illustrate'sectional views of a plastic mask. 116 adapted for use with the permanent magnet arrangement of the present invention. In a television receiver, a mask is conventionally provided for masking off the peripheral region of the cathode ray tube screen and it has been found that such a mask may serve to hold the permanent magnets in proper position with respect to the screen unit of the tube. As shown in Fig. 8, the mask is provided at spaced points about its periphery with arcuate axial flanges which extend inwardly toward the rear of the receiver cabinet. The sectional view of Fig. 8 illustrates the flanges 114 which project from the mask 116. The flanges are formed with seats 118 for receiving snugly the cup 78 with which the permanent magnet 50 is associated. ,A tubular protection 126 of the mask is located betweenthe flanges 114 and slidably receives the shaftll of the magnet- Thus, the slotted end 70" projects outwardly from the front of the mask 115 and is accessible for manipulation. The cup 78 is secured in place between the seats 118 of the flanges 114 as by means of a ring 122 secured to the flanges as by means of screws 124. The ring 122 prevents axial movement of the cup 78 with respect to the flanges 114. As shown in Fig. 4, each of the cups 78 is provided with notches 78'. The notches 78 of the cup 73 receive lugs 128 which are formed in the seats of the flanges 114, so that the stationary lugs 128 prevent rotational movement of the cup 78 in its seat.

, As many magnet mounting flanges as desired may be formed on the mask, as will be understood.

As shown in the vertical sectional view of Fig. 9, the mask 116 further includes an axially and rearwardly extending rim portion 130 which serves as a support for the front end of a cathode ray tube whose screen is denoted by the dotted line 16. The rim 13%} also acts as a safety device insofar as the high voltage applied to the tube is concerned. A plurality of corrugations 132 may be formed in the radial wall of the mask 116 in order to increase the high voltage leakage path of the mask. The safety glass 106 is shown in its normal position with respect to the mask 116.

From the foregoing, it will be appreciated that the plastic mask structure normally provided in a television receiver may be readily adapted to serve additionally as a mount for the plurality of permanent magnets provided in accordance with the present invention for the purpose of minimizing color dilution. The magnet shafts 70 extend forwardly from the mask so that access to the shafts may behad through the simple expedient of removing the bezel which normally covers them. It is to be borne mind, that it is by reason of the novel arrangement of to the influence of the field of said magnet immediately prior to'their impingement upon the discreteelemental areas. of said screen, a rotatable shaft upon which said magnet is secured with its north and south poles extending .-radially in opposite directions therefrom, and means permanently supporting said shaft, and hence said magnet for rotation about a single fixed axis substantially parallel to said tube axis whereby the eflective field of said magnet may be rotated between a'first positionwhereat said field is substantially tangential to said screen to correct for said undesired radial departures of said beam-electrons from their said normal paths and a second position whereat said effective field is substantially radial of said screen to correct for said undesired tangential departures of said beam-electrons from their said normal paths.

2. In combination, a cathode-ray tube having a central ap raovs hold is substantially radial of said screen to'correct for said undesired tangential departures of said beam-electrons from their said normal paths.

3.. In combination, a cathode ray tube of the type including a plane of deflection at which electrons are subjected to a scanning deflection in their transit along the longitudinal axis or" said tube toward a screen unit including a target made up of a plurality of respectively different elemental areas, a permanent magnet having north and south poles, and means permanently supporting said magnet in the region of said screen unit for rotation about a single fixed axis parallel to said longitudinal axis of said tube.

4. In combination, a cathode ray tube of the type including a plane of deflection at which electrons are subjected to a scanning deflection in their transit along the longitudinal axis of said tube toward a screen unit including a target made up of a plurality of respectively different elemental areas, a permanent magnet having north and south poles, means for supporting said magnet in the region of said screen unit for rotation about a single fixed axis parallel to said longitudinal axis of said tube, a member of flux permeable material disposed about a portion of said fixed axis and means for producing relative movement along said axis between said magnet and said member for controlling the eflective intensity of the field of said magnet.

5. in combination, a cathode ray tube of the type including a plane of deflection at which electrons are subjected to a scanning deflection in their transit along the longitudinal axis of said tube toward a screen unit including a target made up of a plurality of respectively different elemental areas, a plurality of permanent magnets,

each of which has a north and south pole; and means permanently supporting said magnets around the screen unit of said tube for rotation about fixed axes parallelto said longitudinal of said tube.

6. In combination, a cathode ray tube of the type including a plane of deflection at which electrons are subjected to a scanning deflection in their transit along the longitudinalaxis of said tube toward a screen unit including a target made up of a plurality of respectively difierent elemental areas, a plurality 'of permanent magnets, each of which has a north and south pole, individual control shafts for supporting said magnets around the screen unit of said tube for rotation each about a single permanently fixed axis parallel to said longitudinal ax'is'of said tube; and means foreflectively controlling the intensity of the field produced by each of said magnets. V, i'

7. In combination, a cathode ray tube of the type ineluding a plane of deflection'at which electrons are subaxis and wherein beam-electrons are subjected to undesired radial and tangential departures fromjtheir norrnfl paths of scan in their transit to discrete elemental areas of an electron-sensitivescreenof the mosaic variety, a permanent magnet having north andsouth poles, a shaft vicinity of saidvmosaic screen for independent axial and rotational movements along and about a single axis substantially parallelto said tube axis whereby the eifece intensity ofthe field between the north and south es of said magnet'may be altered byrnoving said shaft "any toward'and away'from said screen andtheorien i'ected to a scanningv deflection in their transit along the longitudinal axis vof'said tube toward a screen unit including a target made up of a plurality of respectively different elemental areas, a permanent magnet having north and south-poles, and a shaft for supporting said magnet for rotation about a permanently fixed axis parailel to said longitudinal axis, whereby said magnetmay be positioned tangentially of such tubeto produce radial movement of electrons therein and said magnet may be positioned with respect to a .line joining said poles lying Y jected to a scanning deflection at which electronsaresuhjected to a scanning'deflection in their transit along the longitudinal of .said tube toward-a -'screen unit ineluding a target made up of a plurality of respectively difierent elemental area, a permanent magnet having north and south poles, a shaft for supporting said magnet for rotation about a permanently fixed axis parallel to said longitudinal axis whereby said magnet may be positioned tangentially of said tube to produce radial movement of electrons therein and whereby said magnet may be positioned with respect to a line joining said poles lying along a radius of said tube to produce tangential movement of electrons therein; and means for efiectively controlling the intensity of the field produced by said magnet.

9. In a color television receiver of the type which includes a color kinescope having a screen unit including a target made up of a plurality of elemental areas of respectively difierent color light-emitting characteristics and means for producing and directing electrons toward said target and a mask element for obscuring the peripheral portion of said target, apparatus comprising: a plurality of permanent magnets, each having a north and a south pole; and means for supporting said magnets on said mask element in the region of the screen unit of said kinescope for rotation about an axis parallel to the ngitudinal axis of said kinescope.

10. In a color television receiver of the type which includes a cabinet housing a color kinescope having a screen unit which includes a target made up of a plurality of elemental areas of respectively difierent color light-emitting characteristics and means for producing and directing a plurality of electron beam components toward said target, said cabinet having a front panel containing an opening through which such kinescope screen may be viewed; apparatus for controlling the impingement of said beam components upon said screen, said apparatus comprising: a plurality of permanent magnets each having north and south poles at its opposite extremities; a plurality of inflexible control shafts secured, respectively, to each of said magnets intermediate its extremities and at substantially right angles to a line joining said poles; and means including said front panel and said inflexible shafts for supporting said magnets in said cabinet around the screen region of such kinescope for rotation about an axis parallel to the longitudinal axis of said kinescope, said magnetcontrol shafts extending forwardly of said kinescope screen unit and through said front panel for access from the exterior of said cabinet.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,643 De Gier Oct. 14, 1941 2,416,687 Fry Mar. 4, 1947 2,442,975 Grundmann June 8, 1948 2,459,732 Bradley Jan. 18, 1949 2,541,446 Trott Feb. 13, 1951 2,816,244 Hillegass Dec. 10, 1957 2,825,835 Heppner Mar. 4, 1958 OTHER REFERENCES R.C.A. Model 21-CT-55, Service Data 1954, No. T13, first printing November 24, 1954. 

